1. Field of the Invention
The present invention relates to a battery such as a non-aqueous electrolyte battery having an electrolyte injecting port formed on a battery case and plugged by an electrolyte injecting plug.
2. Description of the Related Art
In a conventional small-sized non-aqueous electrolyte battery, an aluminum conical electrolyte injecting plug 8 as shown in FIG. 11 is spot-welded to an electrolyte injecting port 2 formed on the battery case 1 through which an electrolyte has been injected into the battery so that the electrolyte injecting plug 8 is welded to the external edge of the electrolyte injecting port 2 to plug the port.
However, as the size of the battery increases, the diameter of the electrolyte injecting port 2 must be increased. Consequently, it is made more difficult to spot-weld a large-sized electrolyte injecting plug 8 completely to the electrolyte injecting port 2 leaving no gap therebetween. In order to overcome this difficulty with the conventional non-aqueous electrolyte battery, it has been a practice to form a female thread on the electrolyte injecting port 2 as shown in FIG. 13. A male thread formed on the forward end 8a of the electrolyte injecting plug 8 is engaged with the female thread. A packing 9 is provided to be interposed between the flange portion 8b of the electrolyte injecting plug 8 and the outer edge of the electrolyte injecting port 2. Consequently, the electrolyte injecting port 2 through which an electrolyte has been injected into the battery is plugged, as shown in FIG. 13.
Alternatively, the electrolyte injecting plug is fastened to the battery case with a nut on the other side of the electrolyte injecting port 2 instead of forming a female thread on the electrolyte injecting port 2. An O-ring is provided to be interposed between the flange portion 8b of the electrolyte injecting plug 8 and the outer edge of the electrolyte injecting port 2 instead of packing 9. Further, the packing 9 or O-ring may be fitted in an annular groove formed on the inner side of the flange portion 8b. 
However, because the packing 9 or O-ring is made of a rubber or synthetic resin material, it has the following problems. Namely, it is liable to deterioration due to aging and hence denaturation due to contact with the electrolyte or heat generated upon excessive charge and discharge. Accordingly, it may cause the deterioration of the airtightness of the sealed portion resulting in the leakage of the electrolyte.
Further, if the electrolyte injecting plug 8 having a male thread formed at the forward end thereof or a flange portion 8b thereon is used, a large protrusion is formed at the sealed portion to an extent such that it gives an offense to the eye or an obstruction in handling.
It is an object of the present invention to provide a battery which is rendered unsusceptible to deterioration of airtightness of the sealed portion by fitting an electrolyte injecting plug in an electrolyte injecting port and laser-welding the electrolyte injecting plug to the electrolyte injecting port at the periphery thereof.
According to a first aspect of the present invention, a battery comprises: a metallic battery case for housing an electricity-generating element, the metallic battery case having an electrolyte injecting port of an electrolyte; and an electrolyte injecting metallic plug laser-welded to an outer edge of the electrolyte injecting port on a periphery of the battery case, at least a part of the electrolyte injecting metallic plug being inserted into the electrolyte injecting port.
In accordance with the first aspect of the present invention, an electrolyte injecting plug is laser-welded to an electrolyte injecting port at the periphery thereof with its entire part or forward end being inserted therein. In this arrangement, the electrolyte injecting plug can be fixed to the electrolyte injecting port to assure that the electrolyte injecting port is plugged. Further, since the electrolyte injecting plug can be easily welded to the electrolyte injecting port at the periphery thereof by allowing a laser spot to run, the electrolyte injecting port cannot be insufficiently plugged even if the size of the electrolyte injecting port is increased to increase the periphery of the electrolyte injecting plug to be welded. Moreover, since metals are welded to each other to plug the electrolyte injecting port free from packing or O-ring, the airtightness of the sealed portion cannot be deteriorated.
More preferably, the diameter or diagonal distance of the foregoing electrolyte injecting port is not less than 2.5 mm.
According to a second aspect of the present invention, concerning to the battery defined in the first aspect, the electrolyte injecting port is a stepped or tapered round port which is greater outside the battery case than inside the battery case in diameter and the plug inserted in the electrolyte injecting port is a stepped or tapered disc.
In accordance with the second aspect of the present invention, the electrolyte injecting plug can be securely fitted in the electrolyte injecting port and thus cannot fall into the interior of the battery case.
Further, by arranging the electrolyte injecting plug such that the outer surface thereof is almost flush with the surface of the outer edge of the electrolyte injecting port, the outer surface of the electrolyte injecting plug can be prevented from protruding from the battery case. In this arrangement, the electrolyte injecting plug does not give an offense to the eye or an obstruction in handling.
A third aspect of the present invention concerns the battery defined in the first aspect, wherein the electrolyte injecting plug has a forward end protruding into the electrolyte injecting port from the inner side of a flange having a greater diameter or diagonal distance than that of the electrolyte injecting port.
In accordance with the third aspect of the present invention, the flange portion of the electrolyte injecting plug protrudes from the battery case, but the forward end of the electrolyte injecting plug can be securely fitted in the electrolyte injecting port.
Further, the electrolyte injecting plug can form a male thread on the forward end thereof while the electrolyte injecting port can form a female thread on the inner surface thereof to engage with the male thread so that the electrolyte injecting plug fitted in the electrolyte injecting port can be securely fixed thereto.
According to a fourth aspect of the present invention concerns the battery defined in the first or second aspect, wherein both the electrolyte injecting port and the electrolyte injecting plug have a curved portion formed protruding externally at the external edge thereof.
In accordance with the fourth aspect of the present invention, since the provision of a curved portion on the outer edge of the electrolyte injecting port and the electrolyte injecting plug, it is possible to prevent the diffusion of heat during laser welding and hence secure the welding of metal to metal.